Emission of ultrafine copper particles by universal motors controlled by phase angle modulation

Abstract

Laboratory experiments were performed to investigate the emission of particulate matter by electric universal motors controlled by phase angle modulation. The motor of a commercial professional vacuum cleaner (PVC) served as a standard source of the particles. Total number concentrations were measured with a condensation particle counter (CNC), number size distributions with a scanning mobility particle sizer (SMPS) and with a portable optical aerosol spectrometer (PAS). Impactor samples were collected to determine the size-segregated concentrations of mass and of copper. The total number concentration produced by the motor operated at full power input ( ∼ 0.9 kW , rotational speed ∼ 23 , 500 min - 1 ) in a test room (volume 4.2 m 3 , air exchange rate 0.021 min - 1 ) saturates rapidly at 3.0 × 10 11 particles m - 3 within 15 min of operation. The concentrations of the total mass and of copper were, at an air exchange rate of 0.009 min - 1 , 146 and 42 μ g m - 3 , respectively. With a simple box model these concentrations correspond to emission rates of the motor of 2.7 × 10 10 particles min - 1 , 5.4 μ g min - 1 of total mass and 1.6 μ g min - 1 of copper. When phase angle modulation was employed to reduce the power input of the motor, the number concentration was found to be nearly proportional to the jump in the applied voltage and the total number concentration increased by up to a factor of 5 at a rotational speed of ∼ 21 , 300 min - 1 (power input ∼ 0.5 kW ). The number size distributions indicated that the phase angle modulation increases mainly the emissions of ultrafine particles (UFPs) and the impactor samples suggest that these UFPs consist nearly entirely of copper.